Polymerization of butadiene-1, 3 hydrocarbons



. than twelve carbon atoms and at least Patented July 31 1945 UNITEDSTATES PATENT OFFICE 2,380,905 POLYMERIZATION F BUTADIENE-LS HYDROCABBONWilliam D. Stewart, Akron, Ohio,

B. F. Goodrich Company, New

assignor to The York, N. Y., a

corporation of New York No Drawing. Application April 28, 1942, SerialNo. 440,852

13 Claims.

improving the properties of the polymers obtained.

I have discovered that these and other objects may be accomplished bycarrying out the polymerization oi butadiene-LS hydrocarbons in aqueousemulsion in the presence of a sulfur-contaming organic compound, which,for the purposes of this invention, may be defined as an aliphaticorganic compound which contains less one but not more than two divalentsuliur atoms at least one of which is connected to a carbon atom in anopen chain aliphatic radical containing at least one hydrophilic group.By the expression open chain aliphatic radical containing at least onehydrophilic group" is meant just what the expression implies, that is, aradical 01! an open chain aliphatic compound which is substantiallymore.

water soluble than an unsubstituted aliphatic hydrocarbon by reason ofthe iact that it contains one or more hydrophilic groups, or groupswhich impart water solubility to a compound, such as, for example,hydroxy, amino, cal-boxy, thiol, carbonyl, amide, sulionic acid groupsand the like.

Whether or not any given radical contains a hydrophilic group mayreadily be ascertained by comparing the water solubility of the compoundformed by adding a hydrogen atom to the radical with the watersolubility of the corresponding unsubstituted hydrocarbon. For example,the hydrory-ethyl radical obviously contains a hydrophilic group sinceethyl alcohol is water soluble,

whereas ethane is water insoluble. On the other hand, the chloro-ethylradical obviously does not contain a hydrophilic group because ethylchloride is substantially as water insoluble as ethane itseli.

The sulfur-containing compounds in the above deflnedclsssareprincipayoithreetypes, namely:

(1) Compounds containinc less than 12carbonatomsandatleastcnebutnotmorethantwodivalentnflimutomspsuentinathioL-figroupwhichisiinhedtoacarbonatominan open chain aliphatic radicalcontaininl at least (Cl. 260-845) I one hydrophilic group. Typicalexamples of compounds of this type are:

Thioglycollic acid (thiol-acetic acid) H-S-CHx-C-OH Thin-lactic acid(alpha-thiol propionic acid) on'r-cn-c-on Glutathione (glutamylcysteinyl glycine) Beta-mercapto ethanol (beta-thiol ethanol)H-B-CHn-CHr-O-H 1,2-ethane-dithiol (dithioglycol) n-s-cm-cm-s-n2,2-dithio diglycol (3,2-dithiol-ethyl ether) n-s-onr-cnr-o cm-cm-s-nUKP HP H alpha-amino propionic acid) 2,2'-dlamino diethyl sulfideCHz-CHy-NH:

CHz-CHr-NHI Methyl beta-smino-ethyl sulfide C Hr-O H's-NH: Ethylbeta-hydroxy-ethyl sulfide CHy-C H] Dextrose ethyl mercaptal CHr-CHr-S(3) Componds containing less than 12 carbon atoms and two divalentsulfur atoms present in a dlsulfide, --S--S, group which is linked byeach of its disconnected valences to a. carbon atom in an aliphaticradical containing at least one hydrophilic group. Typical examples ofcompounds of this type are:

Di-thio-di-slycollic acid Cystine NH: O

s-cm-n-ti-on -cnrcH-o-on NH: Di-beta-hydroiqr-ethyl disnlfideS-GHr-CHaOH -cn,-cH,0H

Di-beta-amino-ethyl disulilde S-GHr-CHr-NH: -CHr-CHrNlil In the practiceof this invention butadiene-Ltl .hyclrocarbons or mixtures of suchhydrocarbons with other monomers copolymerizable therewith arepolymerized in the form an aqueous emulsion in the resence or a smallamount of a sulfur-containing compound of the character described above,preferably one of the sulfur-containing compounds specifically mentionedabove. The emulsion is conveniently prepared by emulsitying the monomersin water with the aid of an emulsifying agent, and the polymerization isusually eflected by agitating the emulsion at a temperature of about 20to C. In addition to the sulfur-containing compounds of this invention,it is also-desirable that the emulsion contain one or ?more othersubstances which favorably aifect the polymerization such aspolymerization initiators, polymerization modifiers and the like. Thepolymerization products are obtained in theifcrm of latex-likedispersions which may be coagulated in the usual way to yield the solidpolymers:

The metho of this invention may be applied to the poly erizaticn inaqueous emulsion of any of the butadiene-1,3 hydrocarbons, by which ismeant butadiene-l,3, which is ordinary butadiene, and its hydrocarbonhomologs which polymerize in essentially the same manner such asisoprene, 2,3-idimethyl butadiene-l,3, piperylene and the like. Mixturesof such hydrocarbons with one another or with other monomers which arecopolymerizable therewith in aqueous emulsion to form linear copolymersmay also be used. Monomers copolymerizable with butadiene hydrocarbonsinclude aryl olefins such as styrene, p-chloro styrene, p-methoxystyrene. vinyl naphthalene and the like; acrylic and substituted acrylicacids and their esters, nitriles and amides such as acrylic acid, methylacrylate, ethyl acrylate, methyl alpha-chloro acrylate. methylmethacrylate, methyl ethacrylate, ethyl methacrylate, acrylonitrile,methacrylonitrile, methacrylemide and the like; methyl vinyl ketone,methyl isopropenyl ketone, vinylidene chloride, vinyl furane, diethylfumarat-e and other unsaturatd 2ndrocarbons, esters, ethers, nitriles,etc. All these monomers, in general, contain the characteristicstructure where at least two of the disconnected valences are attachedto hydrogen and at least one is connected to an electro-negative group,that is, a group which substantially increases the polar character ofthe molecule. It 13 preferable, in this invention, that these monomerswhen em-- ployed in mixtures with butadiene-i,3 hydrocarbons, be presentin minor proportions by weight since monomer mixtures containing greateramounts of butadiene-l,3 hydrocarmns than of other monomers yieldsynthetic rubber materials on polymerization. However, the invention isapplicable to any mixture of a butadiene-l,3 hydrocarbon with anothermonomer copoiymerizable therewith, which may be copolymerizeid inaqueous emulsion.

The preferred methods of practicing this invention and the improvedresults btained when the sulfur-containing compounds or this inventionare present in the emulsion polymerization oi butadiene-lfi hydrocarbonswill be shown by the following specific examples which illustrate theinvention as applied to the oopoiymerizeition of butadiene andacrylonitrile, but which are not -intended to limit the invention in anyrespect.

Example 1 A mixture of 55 parts of butadiene and 45 parts ofacrylonitzile is emulsified in 250 parts emulsion and the emulsion isagitated at 30 C.

After 40 hours a latex-like emulsion is formed which, upon coagulation,produces a 100% yield of a rubbery copolymer of butadiene andacrylonitrile. The copolymer is plastic and easily milled and, in theserespects, resembles unvulcanized natural rubber. It is 74% soluble inbenzene. When compounded and vulcanized in a standard test recipe ityields vulcanizates having a tensile strength of 5600 lbs/sq. in. and a730% elongation. A similar polymerization in which cystine was notpresent in the emulsion during the polymerization required 45 hours toproduce a 90% yield and the product was not nearly so plastic and easilymilled, more nearly resembling vulcanized natural rubber in theserespects. It was only 24% soluble in benzene and yielded vulcanizateswhich did not possess as high a tensile strength and elongation as thevulcanizates obtained from the product of this example.

Example 2 Example 1 is repeated using, instead of cystine, 0.5 part ofbeta-mercapto ethanol. The polymerization is completed after only 31hours at 30 C., and a rubbery copolymer similar to that obtained inExample 1 is the product.

Example 3 Example 4 A mixture of 55 parts of butadiene and 4., parts ofacrylonitrile is emulsified in 250 parts of a 2% aqueous soap solutionand the resulting emulsion is polymerized at 30 C. after the addition of0.35 part of hydrogen peroxide and 0.5

part of 2,2'-diamino diethyl sulfide.

After 31 hours, the emulsion is polymerized to a latex from which, bycoagulation, a 90% yield of a plastic coherent rubbery copolymer isobtained. Without the presence of the sulfide, the polymerizationrequires 55 hours to produce a 90% yield and the product is tough,non-plastic and diflicult to mill.

The above examples show that the presence of the sulfur-containingcompounds of this invention speeds up the polymerization reaction and,at the same time, produces a rubbery polymer which is more plastic, moresoluble and more easily milled. Other types of sulfur-containingcompounds, not included in the class of sulfur compounds of thisinvention, called polymerization modifiers such as dialkyl dixanthogens,diaryl disulfldes, tetraalkyl thiuram mono and polysulfides, andmercapto thiazoles, are also known to increase the plasticity andsolubility of butadiene polymers and copolymers prepared in theirpresence. However, these polymerization modifiers generally slow downthe speed of the polymerization and, in many cases, inhibit the reactionto such an extent that they cannot be employed unless usedsimultaneously with strong polymerization catalysts.

The following examples illustrate the practice of the invention whenboth a polymerization modifier and a sulfur containing compound of thisinvention are employed in the emulsion during the polymerization.

Example 5.

An emulsion containing the following ingredients is prepared:

Parts Butadiene u 55 Acrylonitrile 45 Sodium myristate (2% aqueoussolution) 250 Hydrogen peroxide .35 Di-isopropyl dixanthogen 0.60Thioglycollic acid .50

The emulsion is then agitated at 30 C. for 22 hours whereupon asynthetic latex is obtained which, when coagulated, produces a 96% yieldof a rubbery copolymer of butadiene and acrylonitrile. The copolymer isquite plastic. soluble in benzene, and may readily be milled on either ahot or relatively cold mill. Moreover, it was noted that the copolymeracquired considerable tackiness after being milled on a hot mill. Whencompounded and vulcanized it yielded vulcanizates having tensilestrengths of 4500-5800 lbs/sq. in. and ultimate elongations of 420-600%.When this example is repeated in the absence of thioglycollic acid thepolymerization requires 45 hours and the polymer obtained is plas c andsoluble but it is not readily milled on a hot-mill.

Example 6 The recipe described in Example 5 is again employed exceptthat 0.50 part of 2,2'-dithio-diglycol are employed in place of thethioglycollic acid. A rubbery polymer which is similar to the polymerdescribed in Example 5 is obtained in yield after a polymerization timeof 22 hours. Similar results are obtained using d-methionine or cysteinein place of 2,2'-dithiodiglycol.

From these examples it is seen that the sulfur-containing compounds ofthis invention accelerate polymerizations carried out in the presence ofa polymerization modifier and, in addition, improve the millingcharacteristics of the polymers obtained.

Although all the above examples have been examples of polymerizationsemploying a fatty acid soap as the emulsifying agent and hydrogenperoxide as the polymerization initiator, it is to be understood thatthis is merely a preferred procedure and that many other emulsifyingagents and initiators may likewise be used.

As emulsifying agents which are useful in the emulsion polymerization ofbutadiene-1,3 hydrocarbons there may be mentioned fatty acid soaps suchas sodium oleate, potassium palmitate and sodium myristate, syntheticsaponaceous materials including hymolal sulfates and alkaryl sulfonatessuch as sodium lauryl sulfate and sodium isopropyl naphthalenesulfonate, and salts of organic bases containing long carbon chains suchas trimethyl-cetyl-ammonium methyl sulfate, the hydrochloride ofdiethylaminoethyloleylamide and the like. The soaps are employed inpolymerizations under basic conditions, the salts of organic bases underacid conditions and the synthetic saponaceous materials under acid,alkaline or neutral conditions.

Polymerization initiators which may be employed in the emulsion togetherwith the sulfurcontaining compounds of this invention includeper-compounds such as hydrogen peroxide, benzoyl peroxide, potassiumper-sulfate, sodium perborate, sodium periodate, potassium percarbonateand the like as well as other types of initiators such asdiazoaminobenzene, sulfur dioxide, dipotassium diazomethane disulfonate,triphenylmethylazobenzene, sodium cobatinitrite and the like.

The following examples illustrate the practice of the invention withemulsifying agents other than fatty acid soaps and polymerizationinitiators other than hydrogen peroxide.

Example 7 A mixture of 55 parts of butadiene and 45 parts ofacrylonitrile is mixed with 250 c. c. of a 2% aqueous solution of sodiumlauryl sulfate, 2 parts of sodium periodate and 0.5 part ofbeta-mercapto-ethanol. The resulting emulsion is polymerized at 30 C.The polymerization is complete in 90 hours, although in the absence ofbetamercapto ethanol 110 hours are required. When a polymerizationmodifier such as di-isopropyl dixanthogen is also present in theemulsion during the polymerization a plastic, soluble, easily milledsynthetic rubber is obtained but in the absence of beta-mercapto ethanolthe di-isopropyl dixanthogen does not appreciably improve the plasticityof the polymers obtained by this type of polymerization.

Example 8 A mixture of 88 parts of butadiene and 72 parts ofacrylonitrile is emulsified in 250 parts of a3% aqueous solution of asodium alkyl naphthalene sulfonate which is buffered with sodiumphosphate to a pH of about 4. After addition of 2 parts of potassiumpersulfate as a polymerization initiator and 1.5 parts of cysteine, theemulsion is polymerized. The polymerization time is 23 hours at 30 C. Inthe absence of cysteine the polymerization requires 56 hours at 30 C.The latex obtained by the polymerization of this example may be driedtoyield tough, oil resistant synthetic rubber films or it may becoagulated to yield a plastic oil resistant synthetic rubber.

The amount of the sulfur-containing compounds of this invention to beused in the emulsion polymerization of butadiene-1,3 hydrocarbons may bevaried over rather wide limits depending upon the particular compoundused but, in general, it is preferable that less than 3% of the sulfurcompound based on the weight of the monomers be employed. Amounts lessthan 1% are generally sufilcient to eiTect an increase in the speed ofthe polymerization but it is often desirable to employ as much as 3% oreven more of the sulfur-compound when a large increase in the solubilityand plasticity of the polymers is to be effected.

The catalytic effect of the sulfur-containing compounds herein describedmay further be enhanced by employing a catalytic combination of thesulfur compound with a heavy metal salt or by employing complexcompounds containing a heavy metal atom united in complex formation withsuch sulfur compounds. In this event the time required for thepolymerization is decreased far beyond that which could be attained byusing a heavy metal salt or the sulfur compound alone. For instance, thepolymerization described in Example 2 is 90% completed in only 10 hourswhenferrous ammonium sulfate is employed in combination withbeta-mercapto ethanol. Other heavy metal salts such as those of cobalt,nickel,

mercury, copper and the like bring about similar reductions in thepolymerization time. The use of catalytic combinations of heavy metalcompounds with these sulfur-containing compounds is more fully disclosedand claimed in my copending application Serial No. 379,715, filedFebruary 19, 1941.

Other embodiments of this invention wherein other monomer mixtures arepolymerized also show that the sulfur-containing compounds of thisinvention decrease the time required for polymerizations and improve theproperties of the polymers obtained. For example, a mixture of 70 partsof butadiene and 30 parts of styrene may be polymerized in aqueousemulsion in the presence of the sulfur-compounds of this invention in ashorter time and more desirabl rubbery copolymers are obtained than whensuch compounds are not present. The same is true when methyl acrylate,methyl methacrylate, isopropenyl ketone, vinylidene chloride and othermonomers are used in place of styrene.

Another distinct advantage to be gained by the practice of thisinvention is that the presence of these sulfur compounds permitspolymerizations to occur which would otherwise not take place because ofthe presence of some inhibitor. Many inhibiting substances are quitediificult to exclude from the polymerization batch since they may bepresent as impurities in the monomers, in the water employed or in otheressential ingredients. For this reason the sulfur-compounds of thisinvention are often referred to as detoxifying agents.

Other methods and procedures known to be useful in connection with thepolymerization of butadiene-l,3 hydrocarbon in aqueous emulsion arewithin the spirit and scope of the invention as defined in the appendedclaims.

I claim:

1. The method which comprises subjecting a monomeric material comprisingbutadiene-L hydrocarbon material, as the sole diene material present, topolymerization in aqueous emulsion in the presence of an aliphaticorganic compound which contains less than twelve carbon atoms and atleast one but not mor than two divalent sulfur atoms at least one ofwhich is connected to a carbon atom in an open chain aliphatic radicalcontaining at least one hydrophilic group.

2. The method which comprises subjecting a .monomeric mixture comprisinga butadiene-1,3

hydrocarbon, as the sole butadiene present, and a monomer which containsa single group and is copolymerizable therewith in aqueous emulsion, topolymerization in aqueous emulsion in the presence oi! an aliphaticcompound containing less than twelve carbon atoms and containing a thiolgroup connected to an aliphatic radical containing a carboxylic acidgroup.

4. The method which comprises subjecting a monomeric mixture consistingof butadiene-L and a monomer which contains a single group and iscopolymerizable therewith in aqueous emulsion, to polymerization inaqueous emulsion in the presence of an aliphatic compound containingless than twelve carbon atoms and containing a thiol group connected toan aliphatic radical containing an hydroxy group.

5. The method which comprises subjecting a monomeric material comprisingbutadiene-l,3 hydrocarbon material, as the sole diene material present,to polymerization in aqueous emulsion in the presence oi thioglycollicacid.

6. The method which comprises polymerizing a butadiene-l,3 hydrocarbonin aqueous emulsion in the presence of beta-mercapto ethanol.

7. The method which comprises subjecting a monomeric mixture comprisinga butadiene-l,3 hydrocarbon, as the sole butadiene present, and amonomer which contains a single group and is copolymerizable therewithin aqueous emulsion, to polymerization in aqueous emulsion in thepresence of an aliphatic compound which contains less than twelve carbonatoms and two divalent sulfur atoms present in a disulfide group whichis linked by each of its disconnected valences to a carbon atom in analiphatic radical containing at least one hydrophilic group.

8. The method which comprises subjecting a monomeric mixture consistingof butadiene-L and a monomer which contains a single and a monomer whichcontains a single group and is copolymerizable therewith in aqueousemulsion, to polymerization in aqueous emulsion in th presence ofcystine.

10. The method which comprises polymerizing in aqueous emulsion amixture of a butadiene-l,3 hydrocarbon as the sole butadiene present,and a compound which contains a single group and is copolymerizabletherewith in aqueous emulsion in the presence of an aliphatic organiccompound which contains less than twelve carbon atoms and at least onebut not more than two divalent sulfur atoms at least one of which isconnected to a carbon atom in an open chain aliphatic radical containinga, hydrophilic group.

11. The method which comprises polymerizing a mixture 01' bu-tadiene-l,3and acrylonitrile in an aqueous emulsion in the presence of twoglycollicacid.

12. The method which comprises polymerizing a mixture of butadiene-l,3and acrylonitrile in an aqueous emulsion in the presence of betamercaptoethanol.

13. The method which comprises polymerizing a mixture of butadiene-L3and acrylonitrile in an aqueous emulsion in the presence of cystine.

WILLIAM D. STEWART Certificate of Correction Patent N0. 2,380,905. July31, 1945.

' WILLIAM D. STEWART It is hereby certified that errors appear in theprinted specification of the above numbered patent requiring correctionas follows: Page 2, second column, line 61, for

copolymerizeid read copolymerized; line 69, for copolymerizeition readcopolymerization; page 3, first column, line 43, for 4 read 45; and thatthe said Letters Patent should be read with these corrections thereinthat the same may conform to the record of the case in the PatentOffice.

Signed and sealed thiellth day of June, A. D. 1946.

LESLIE FRAZER,

First Assistant Commissioner of Patents.

